1. Field of the Invention
The present invention relates to an ultrasound unit in which ultrasound elements each including capacitive micro-machined ultrasound cells formed on a semiconductor substrate are disposed on a package member via an insulation member, and an ultrasound endoscope including the ultrasound unit.
2. Description of the Related Art
Ultrasound diagnosis in which a diagnosis is made by applying ultrasound to an object to be examined to form an image of a state of the inside of the body from echo signals is widespread. An ultrasound endoscope system is one of diagnostic apparatuses used for ultrasound diagnosis. An ultrasound endoscope includes an ultrasound unit disposed at a distal end portion of an insertion portion to be inserted into a body. The ultrasound unit has a function that converts electric signals to ultrasound and transmits the ultrasound to the inside of the body and receives the ultrasound reflected by the inside of the body and converts the ultrasound to electric signals.
As an ultrasound cell for an ultrasound unit, Japanese Patent Application Laid-Open Publication No. 2006-50314 discloses a capacitive micro-machined ultrasonic transducer (cMUT) manufactured using an MEMS technique.
An ultrasound cell for a cMUT transmits/receives ultrasound by means of vibration of a membrane including an upper electrode arranged facing a lower electrode via a cavity. In transmission, upon application of a voltage between the electrodes, the upper electrode is pulled to the lower electrode by an electrostatic force, whereby the membrane including the upper electrode is deformed. When the voltage application ceases, the membrane recovers to its original shape by means of an elastic force. Ultrasound is generated by the deformation/recovery of the membrane.
On the other hand, in reception, the membrane is deformed by received ultrasound energy, whereby a distance between the upper electrode and the lower electrode changes. Using a change of a capacity C1 of a capacitor formed by the upper electrode and the lower electrode by ΔC, the received ultrasound energy is converted to an electric signal.